Flame resistant fabrics

ABSTRACT

The present invention provides a woven flame resistant fabric comprising dissimilar warp and fill yarns, the warp yarns comprise staple or filament fibers and have a Limiting Oxygen Index of at least 27, and the fill yarns comprise natural fibers and wherein the ratio of warp to fill yarn ends in the fabric is at least 1.0.

BACKGROUND OF THE INVENTION

[0001] Fabrics made of high temperature and flame resistant fibers havebeen very useful in protective apparel. Although many advances have beenmade in designing comfortable fabrics and garments made from thesefibers, there are still certain aesthetic and subjective reasons todesire flame resistant apparel which also incorporate natural fibers. Tomeet this need, fabrics have been made from combination yarns, that isyarns containing both natural and high temperature and flame resistantstaple fibers. Although fabrics made from such combination yarns may bemade into comfortable garments, the fabric's resistance to hightemperature and flame has been reduced to such an extent that theaddition of flame retardants are necessary to enhance the thermalprotection of the fabric. Typically flame retardants are applied to thenatural staple fibers or the fabrics made from these combination yarnsas topical treatments. The addition of topical treatments may add weightand often stiffness to the fabric as well as provide only temporaryeffectiveness since such treated fabrics tends to lose this protectionwith wash and or wear cycles.

[0002] The object of the present invention is to provide a fabriccombining flame resistance and comfort that may be formulated in a wayto balance thermal performance and cost.

[0003] Another object of the present invention is to provide acomfortable, flame resistant and cost efficient fabric that does notrequire the use of topical flame retardant treatments.

[0004] Another object of the present invention is to provide a strongfabric where flame resistance and cost may be balanced.

[0005] Fabrics have been made from combination yarns to achieve certainfabric properties. U.S. Pat. Nos. 4,941,884 and 4,900,613 to Greendisclose comfortable fabrics of high durability made from warp yarnscontaining a blend of at least 15% by weight high modulus and at least30% by weight low modulus fibers woven with fill yarns containing lowmodulus fibers (usually cotton). Blended high and low modulus fiberswere required in the warp yarns to provide proper shrinkage forincreasing the abrasion resistance.

[0006] Canadian Patent No. 1034842 discloses a protective fabriccomprising interwoven warp and weft threads of dissimilar propertieswith an asymmetric weave, changing from one surface of the fabric to theopposite surface of the fabric to achieve varying energy absorptionproperties throughout the depth of the fabric.

[0007] European Patent Application 310,199 discloses a bulletproof wovenfabric made from filaments or yarns having high strengths and highmoduli and consisting of polymers of ultrahigh molecular weights,wherein the warp filaments or yarns consist of other polymers than theweft filaments or yarns.

[0008] Both UK Patent Application 2,025,789 and Japanese PatentApplication Publication Sho 59(1984)-9053 disclose fabrics reinforced bythe insertion or substitution, at some frequency in the fabric, ofhigher strength adjacent yarns in the warp and/or weft directions.Japanese Patent Application Sho 62-26900 teaches a reinforced aramidfabric having groups of low strength yarns inserted or substituted inthe fabric weave in the warp and/or weft directions. Such reinforcedfabrics are designed for increased tear resistance and have not beendesigned with considerations for comfort or thermal protection.

SUMMARY OF THE INVENTION

[0009] The present invention provides a woven flame resistant fabriccomprising dissimilar warp and fill yarns, the warp yarns comprisestaple or filament fibers and have a Limiting Oxygen Index of at least27, and the fill yarns comprise natural fibers and wherein the ratio ofwarp to fill yarn ends in the fabric is at least 1.0. More preferred arewarp yarns have a Limiting Oxygen Index of 28 or more.

[0010] In the present invention the fibers of the warp yarn may have amodulus of from about 100 to 800 g/dtex. Although fibers moduli of from100 to about 250 g/dtex may be preferred for some uses.

[0011] It is preferred that the warp yarn comprises fibers selected fromthe group consisting of aramid, polybenzimidazole, polybenzoxazole,melamine, poly(phenylene sulfide),polybenzothiazoles, polyimide,polyetherimide, polyamidimides, novaloid and modacrylic fibers and thefill yarn fibers are selected from the group consisting of cotton, silk,wool, rayon and FR rayon. The warp yarn may be formed of fibers that arem-aramid or p-aramid fibers or mixtures of these fibers and may alsoincorporate about 5% by weight or less electrically conductive fiber,particularly sheath-carbon-core fibers.

[0012] A preferred fabric for protective apparel is a fabric wherein thefibers of warp yarn are sulfonated para-aramid fibers and the fill yarnis cotton. P-aramid fibers having a modulus of from 100 to not more than200 g/dtex are particularly useful in fabrics for protective apparel andgarment uses.

[0013] The present invention also provides protective apparel comprisinga woven flame resistant fabric having dissimilar warp and fill yarns,the warp yarns comprise staple or filament fibers and have a LimitingOxygen Index of at least 27, and the fill yarns comprise natural fibersand wherein the ratio of warp to fill yarn ends in the fabric is atleast 1.0.

[0014] It is preferred for the apparel use that the woven fabriccontains warp yarn fibers selected from the group consisting of aramid,polybenzimidazole, polybenzoxazole, melamine, poly(phenylenesulfide),polybenzothiazoles, polyimide, polyetherimide, polyamidimides,novaloid and modacrylic fibers and the fill yarn fibers are selectedfrom the group consisting of cotton, silk, wool, rayon and FR rayon.Useful protective apparel may be made where the warp yarn fibers arem-aramid and the fill yarn fibers are FR rayon. More preferred isprotective apparel where the warp yarns are p-aramid fibers having amodulus of from 100 to about 250 g/dtex. Most preferred is protectiveapparel where the warp yarns are sulfonated p-aramid fibers and the fillfibers are cotton.

[0015] In protective apparel of claim 11 the warp yarn may furthercomprise about 5% by weight or less of an electrically conductive fiber.And for protective apparel it is preferred that the warp yarns arestaple fibers.

DETAILED DESCRIPTION

[0016] This invention provides flame resistant woven fabrics, where theyarns used for the warp and the fill (or weft) are not alike. Thisfabric may be used in protective apparel or for tents, tarps and otheruses where a balance of fabric stiffness, fabric durability, hightemperature, flame resistance, and low cost are desired.

[0017] In the subject fabric, warp yarn fiber selection provides thefabric with high temperature and flame resistance, while fill yarnselection provides the comfort and cost efficiency. In these wovenfabrics, the warp yarns partially cover protect the fill yarns. And itis believed that the warp yarns thereby protect the fill yarns fromflame and high temperature. Therefore, by selecting the warp yarns to beonly those yarns that have an LOI of 27 or more, the warp yarns providethermal protection to both the fill yarns and to the fabric as a whole,thus fill yarns may then be selected to have the properties that makethe fabric comfortable and cost effective.

[0018] In the present invention, the warp yarns are made hightemperature and flame resistant fibers. High temperature and flameresistant fibers those fibers having a Limiting Oxygen Index (LOI) of atleast about 27, and preferably 28 or more. Preferred fill yarns areyarns made from natural fibers, but fill yarns could be selected fromnatural or synthetic fibers. Special consideration must be given theselection of fill and warp yarns to provide a fabric that is suitablefor a protective apparel. Even with these special considerations,fabrics of the present invention encompass a wide selection of yarns,and provide strong, comfortable and durable fabrics that meet militaryand industrial standards for high temperature and flame resistance.

[0019] For fabrics suitable for protective apparel, fill yarns of thisinvention are selected from natural fibers. Natural fibers are thosefibers found or derived from nature, including fibers such as cotton,rayon, and other cellulose based fibers as well as those fibers whichare deemed to have some natural flame retarding properties, such as wooland silk. Rayon spun containing a flame retardant (known as FR rayon) isparticularly useful in the present invention. Nylon, polyester and othersynthetic fibers which melt on exposure to high temperature are notsuitable when used as a major component in a fill yarn for a protectiveapparel fabric. Since these fibers melt on exposure to hightemperatures, their presence may contribute to or aggravate burns.

[0020] In fabrics designed for uses other than protective apparel,fibers from polymers such as nylon and polyester may be acceptable foruse when blended with natural fibers.

[0021] Fill yarns of the present invention may also contain electricallyconductive fibers such as synthetic sheath-carbon-core staple orcontinuous filament fibers. Such fibers reduce the possibility ofsparking and are much preferred over fibers having a topical antistatictreatment. It is recommended that such sheath-core fibers be used at aconcentration of 5% by weight.

[0022] The warp yarns in the present invention must have an LOI of 27 ormore. High temperature and flame resistant fibers useful in the presentinvention for making protective apparel fabrics include, for example,aramid, polybenzimidazole, polybenzoxazole, melamine, poly(phenylenesulfide),polybenzothiazoles, polyimide, polyetherimide, polyamidimides,novaloid and modacrylic fibers. These fibers decompose without theproduction of noxious fumes when exposed to flame. Useful fibers includethose sold under the trademarks: Kevlar (E. I. DuPont, NOMEX (E. I.DuPont), BASOFIL (BASF), TECHNORA (Akzo) KYNOL(Carborundum) and RYTON(Phillips Chemical Company).

[0023] The warp yarn as a whole must have a LOI of 27 or more for thefabrics of the present invention. The actual selection of fibers used tomake the warp yarn will be determined by the Thermal ProtectivePerformance Test (TPP)or other evaluation standards that the fabric isrequired to meet. For example, actual exposure conditions ortemperatures and the length of the exposure (time) will influence theselection of fibers used in the warp and /or the fill. In some cases thewarp may contain up to as much as 30% by weight fibers having an LOI ofless than 27, while the warp yarn as a whole has an LOI of 27 or more.

[0024] Warp yarns of the present invention may also contain electricallyconductive fibers such as synthetic sheath-carbon-core staple orcontinuous filament fibers. Such fibers reduce the possibility ofsparking and are much preferred over fibers having a topical antistatictreatment. Non-permanent topical treatments compromise the performanceof the fabric of the present invention which is inherently heat andflame resistant. When sheath-core electrically conductive fibers areincorporated into the warp yarn, it is recommended that theconcentration of these fibers be about 5% by weight or less in the warpyarn.

[0025] For maximum comfort, staple yarns are preferred for the warp yarnand for the fill yarns.

[0026] High or low modulus fibers may be used in the warp yarns of thepresent invention since fiber modulus is not an essential considerationin these fabrics. The Warp yarn fibers having a modulus of from 100 to800 g/dtex are suitable for use in the present invention. Lower modulusfibers, that is those fibers having a modulus of less than 250 g/dtex orin the range of 100 to 200 g/dtex are preferred for apparel fabricswhich are in direct contact with the wearer so that the fabric hasadequate comfort. Higher modulus fibers may be acceptable for use infabrics that are to be used for specific purposes or in specificlocations within a garment where wearer comfort is of less importance.

[0027] Particularly useful in the fabrics of the present invention arethe m- and p-aramid fibers. Such fibers include high modulus fibers suchas disclosed in U.S. Pat. No. 3,767,756 to Blades. Fibers having lowermoduli include those made by the processes disclosed in U.S. Pat. No.5,336,734 to Bowen et al., U.S. Pat. No. 5,330,698 to Allen et al. &U.S. Pat. No. 3,671,542 to Kwolek. Since the use of the fibers having alower modulus provides a fabric of improved comfort, p-aramids havingmoduli in the range of from about 100 to less than 200 g/dtex arepreferred. Most preferred are the sulfonated p-aramid made according toin U.S. Pat. No. 5,336,734.

[0028] The aramid fibers may be made from homo or co-polymers. The onlyrequirement is that the warp yarn have an LOI of 27 or more.

[0029] It is desirable for strength and durability that the warp yarnsbe made from fibers which are all one type of high temperature and flameresistant polymer. For example, the warp yarn may be 100% by weightp-aramid. Where maximum mechanical strength is not important, warp yarnsmade from mixtures of high temperature and flame resistant fibers may beused. The use of mixed staple fibers may also provide additional comfortor aid in providing additional thermal performance. For example, acommercial blend of 5% by weight p-aramid and 95% by weight m-aramidfiber yarns is used for its improved thermal performance over 100%m-aramid yarns. Another useful blend of p-and m- aramid fibers for thewarp yarn is 60% by weight p- aramid, 40% by weight m-aramid. Staplefibers made from stretch broken continuous filament fibers as well ascut staple fibers may be used in making the warp yarns of the presentinvention.

[0030] The warp yarns themselves may be of different polymercompositions or could be made from plys of different staple yarns orcontinuous filament fibers so long as the warp yarns meet the LOIrequirement. Selection of warp yarns or fiber mixtures for warp yarnsemployed in the design of the fabrics of the present invention may beused to achieve an overall fabric flame resistance that meets variousindustry requirements or standards. Thus, a fabric of the desiredcomfort, durability, cost and flame resistance can be designed accordingto the present invention for specific situations.

[0031] Unless the fabric is intended for a non-garment use, flameresistant or retardant topical treatments applied to fabrics are notrecommended for use in the present invention since these fabrictreatments stiffen the fabric, decrease wearer comfort and tend to betemporary in nature.

[0032] Again to achieve maximum fabric mechanical strength, fill yarnsaccording to the present invention are typically made from one type ofnatural fiber, for example 100% cotton fill yarns. Where maximummechanical strength is not essential, mixtures of staple fibers may beused in the fill yarns, for example, fill yarns containing cotton andwool.

[0033] The ratio of warp ends per inch to fill ends per inch in thefabrics of the present invention range from 1 to about 3, and a range of1 to 2.5 is preferred. For garment use, this ratio range is essentialsince fibers in the warp yarns and the fibers in the fill yarns worktogether not only to provide flame resistance and durability but alsocomfort. In the present invention it is preferred that all warp yarnfibers are inherently flame resistant, that is the warp yarns containingonly fibers having an LOI of 27 or more. It is preferred that the fillyarns be from natural fibers. Although there is no limitation on the LOIof the fill yarn fibers, fill yarns may, if desired have an LOI of 27 ormore.

[0034] The present invention provides a cost effective flame resistantfabric that may be designed for both comfort and mechanical performance.

[0035] The fabrics of this invention are useful in various protectivegarments, including fireman's turnout coats, military apparel andvarious types of protective overalls. Further, these fabrics can be madeinto shirts, pants, and other apparel normally worn in industrial orhazardous environments. The fabrics of this invention may also be usefulin non-garment applications where one desires to balance thermalprotection and cost. Tarps, tents or other fabrics used to cover andprotect people or property may be made from the fabrics of the presentinvention.

[0036] The present invention is illustrated in the following examplewhich is not intended to limit the invention.

EXAMPLES

[0037] Plain weave, ripstop fabrics were prepared from the followingyarns and were woven according to MIL-C-4436.

[0038] Yarns were as follows: the yarns identified as m-aramid arestaple fiber yarn of 100% poly(phenyleneisophthalamide); thoseidentified as Z200 are staple yarns of sulfonated p-aramid fiber sold byE. I. DuPont of Wilmington, DE as Z200; FR rayon indicates fireretardant rayon staple yarns; blends of fiber in staple yarns areidentified by the fibers in the blend. These are nylon/cotton; blends ofm-aramid/cotton and blends of m-aramid/cotton/Z200 and blends ofZ200/cotton. (NOMEX is a registered trademark of E. I. DuPont.)

[0039] The resulting fabrics were tested for grab strength(ASTM-D-5034;results are reported in pounds(lbs)); trapezoidal tear strength(ASTM-D-5733; results are reported in pounds(lbs)); Elemdorf tearstrength (ASTM D1424; results are reported in pounds(lb.)); Taborabrasion( ASTM-D-1044; results are reported in cycles to failure) andThermal Protective Performance, TPP (method reported in Fire TechnologyV. 13 N.1 Feb. 1977; results are reported in seconds times 2 (s×2) to asecond degree burn).

[0040] The control fabric was a commercial fabric of 50% nylon and 50%cotton yarn in both the warp and fill direction. This fabric wasselected as the control because it is a durable and comfortable fabricused to make garments for military, industrial and general workgarments. It is a strong, durable and comfortable fabric, but does notprovide thermal protection. As the Table below shows, the use of warpyarns according to the present invention provides a fabric havingsurprising thermal protection properties combined with strength anddurability.

[0041] The data is summarized in the Table, below. TABLE FABRICEVALUATION Fabric Sample A B C D E Control fill 100% FR 97/3* 100% 70/3050/50 50/50 yarns: rayon FR rayon/ cotton Z200/ m-aramid/ nylon/ nyloncotton cotton cotton Warp 100% 100% Z-200 70/30 50/50 50/50 yarns:m-aramid m-aramid Z200/ m-aramid/ nylon/ cotton cotton cotton Fabric 7.07.1 6.0 4.5 6.1 6.8 Weight w/f, 2.5/1 2.5/1 1.9/1 1.5/1 2.3/1 2/1 endsGrab, 284/73 268/77 285/42 130/63 98/90 264/165 w/f Trap 95/14 91/2755/6 17/12 15/7.5 60/24 Tear, w/f Elm. 8.3/11 8.9/19 14+/ 13/10 7.6/6.314/12 Tear, 12.2 w/f Tabor 588 — 760 465 — 1300 TPP 12.8 14.1 11.5 10.0— — sec Ignite N N N Y Y Y in air

[0042] In the Table, fabric weight is shown in oz/yd², Grab Strength(Grab), Trapezoidal Tear (trap tear)and Elemdorf Tear are in pounds;Tabor Abrasion (Tabor) is in cycles to failure. The term w/f means theresult reported in the warp and then the fill direction. The warp andfill yarn compositions are reported in weight % of the respective yarn.The ratios are shown as weight % as indicated. For example 50/50nylon/cotton means a 50% by weight mix of nylon fibers with a 50% byweight mix of cotton fibers were used in making the yarn. Ignite in airmeans ignition in air. The result is reported as either yes (Y) orno(N). If the fabric does not ignite, it means that the fabric, afterbeing exposed to a flame for 3 to 5 seconds, did not ignite and continueto burn.

[0043] The fabric samples A, B and C are fabrics of the presentinvention. Samples D and E are present to provide a comparison betweenfabrics of the present invention and fabrics made according to prior artmethods of making thermally protective fabrics. Samples D and E arewoven from intimately blended staple yarns.

[0044] Comparing Samples C and D, one sees that both fabrics have theabout same weight ratio of Z200 to cotton in the fabric, but thedistribution of the high LOI fiber is distinctly different. In C thehigh LOI fiber is distributed over the fabric surface with the cotton inthe interior fill yarns; while in D, unlike in C, cotton is present andevenly distributed on the fabric surface. In addition, in C the warpyarns are all Z200 while the fill yarns are all cotton. These warp andfill yarns are stronger than the intimately blended staple yarns of D.For example, comparing the average of the warp and fill data shows thefollowing for C/D respectively, Grab,164/96; Trap Tear, 31/14; and Elm.,14/12. Looking to the test results, the difference in surfaceflammability as measured by the ignition in air test is very differentfor C compared to D.

[0045] Comparing strength data for C and D by averaging the warp andfill values reported above, C is a stronger fabric than D. Both fabricsare about equal to one another in the TPP test.

[0046] Fabrics A and B compared to E show the same differences as thoseof the C and D comparison, that is in each case a stronger fabric thatdoes not ignite in air.

What is claimed is:
 1. A woven flame resistant fabric comprisingdissimilar warp and fill yarns, the warp yarns comprise staple orfilament fibers and have a Limiting Oxygen Index of at least 27, and thefill yarns comprise natural fibers and wherein the ratio of warp to fillyarn ends in the fabric is at least 1.0.
 2. The fabric of claim 1wherein the warp yarns have a Limiting Oxygen Index of 28 or more. 3.The fabric of claim 1 wherein the fibers of the warp yarns have amodulus of from about 100 to 800 g/dtex.
 4. The fabric of claim 1wherein the fibers of the warp yarn have a modulus of from 100 to about250 g/dtex.
 5. The fabric of claim 1 wherein the warp yarn comprisefibers selected from the group consisting of aramid, polybenzimidazole,polybenzoxazole, melamine, poly(phenylene sulfide),polybenzothiazoles,polyimide, polyetherimide, polyamidimides, novaloid and modacrylicfibers and the fill yarn fibers are selected from the group consistingof cotton, silk, wool, rayon and FR rayon.
 6. The fabric of claim 1wherein the fibers of the warp yarn are m-aramid or p-aramid fibers ormixtures of these fibers.
 7. The fabric of claim 1 wherein the warp yarnincorporates about 5% by weight or less electrically conductive fiber.8. The fabric of claim 6 wherein 60% by weight of the warp yarn fibersis p-aramid and 40% by weight are m-aramid fibers.
 9. The fabric ofclaim 1 wherein the fibers of warp yarn are sulfonated para-aramidfibers and the fill yarn is cotton.
 10. The fabric of claim 1 whereinthe fibers of the warp yarn are m-aramid or p-aramid fibers or mixturesof these fibers and wherein the p-aramid fibers have a modulus of from100 to not more than 200 g/dtex.
 11. The fabric of claim 1 wherein thewarp yarn fibers are m-aramid and the fill yarn fibers are FR rayon. 12.Protective apparel comprising a woven flame resistant fabric havingdissimilar warp and fill yarns, the warp yarns comprise staple orfilament fibers and have a Limiting Oxygen Index of at least 27, and thefill yarns comprise natural fibers and wherein the ratio of warp to fillyarn ends in the fabric is at least 1.0.
 13. The protective apparel ofclaim 12 wherein the woven fabric contains warp yarn fibers selectedfrom the group consisting of aramid, polybenzimidazole, polybenzoxazole,melamine, poly(phenylene sulfide),polybenzothiazoles, polyimide,polyetherimide, polyamidimides, novaloid and modacrylic fibers and thefill yarn fibers are selected from the group consisting of cotton, silk,wool, rayon and FR rayon.
 14. The protective apparel of claim 12 whereinthe warp yarn fibers are m-aramid and the fill yarn fibers are FR rayon.15. The protective apparel of claim 12 wherein the warp yarn fibers arep-aramid wherein the p-aramid fibers have a modulus of from 100 to about250 g/dtex.
 16. The protective apparel of claim 12 wherein the warp yarnfurther comprises about 5% by weight or less of an electricallyconductive fiber.
 17. The protective apparel of claim 12 wherein thewarp yarns are staple fibers.
 18. A tarp or tent comprising the fabricaccording to claim 1 .